The present invention relates to an improved cylindrical key and method for its production.
In the production of the early cylindrical key as shown in FIG. 1, a key cylinder 32 is produced by means of a lathe from a metal bar having an axial protrusion rib 321 formed on the periphery thereof, and a groove 322 is then formed on the said protrusion rib by means of a milling machine and an inward protruding key 324 is formed on the cylinder wall below the groove 322 by means of a press. Alternatively, as shown in FIG. 2, the said key cylinder is produced by means of a lathe from a circular cross-section metal bar, and an outward protruding wing 323 and an inward protruding key 324 are formed on the cylinder wall by means of a press. The key cylinder 32 is then secured onto a key plate 31 by means of welding or press fit in order to form a cylindrical key 30. However, such production method has following disadvantages:
(1) It is difficult to process a cylinder with a protrusion rib by means of lathe tool, and hence its production rate is low, and the wear of used lathe tool is great, and its rejection rate is too high, because the cost for forming metal bar is very high, and the accuracy of its outer diameter dimension is difficult to control.
(2) The outward protruding wing 323 and the inward protruding key 324 will be stuck in the groove of the die during press work. This will cause a difficult withdrawal of the work piece, a difficult press work and a difficult control of the product accuracy. In addition, the outward protruding wing 323 and the inward protruding key 324 can not be formed at the same time, and hence the total production cost is increased. In view of these disadvantages, an improved production method is used in substitution for such production method.
In an improved production of a conventional cylindrical key 20 which is also comprised of a key plate 21 and a key cylinder 22. The key plate 21 comprises a plate 210 which is formed with a square hole 211 at one end thereof, and has a protrusion part 212 formed, which comprises an outward protruding wing 213 and an inward protruding key 214. The key cylinder 22 is made of a solid circular cross-section bar, and processed by means of the lathe work in order to form a cylinder 220 with a reduced solid bar end 221 for engagement with the lock hole 811 and the spindle 82 of a lock 80 (as shown in FIG. 1), and the square hole 211 of the key plate 21 respectively. The solid bar end 221 is formed with a cross groove 224 by means of the milling work, which has a width corresponding to the thickness of the key plate 21. The cylinder 220 is formed with a rectangular hole 223 opposite to the cross groove 224 of the solid bar end 221 by means of the press work. When in assembly, the protrusion part 212 is inserted into the rectangular hole 223 of the key cylinder 22 with a small groove 215 between the outward protruding wing 213 and the inward protruding key 214 rested against the cylinder wall of the rectangular hole 223, and also with the square hole 211 of the plate 210 inserted into the cross groove 224 of the key cylinder 22. The two side walls of the cross groove 224 are then pressed by a press in order to firmly hold the key plate 21, and to finish the assembly of a cylindrical key 20. However, such production method has following disadvantages: (1) The fixation of key plate and key cylinder is not firm, because only a small part of the end wall of the square hole 211 of the key plate 21 is held by the two side walls of the cross groove 224 of the key cylinder 22, hence a loose fixation will be produced after they have been used for a short period. (2) When it is in assembly, the two side walls of the cross groove of the key cylinder should be pressed by the press and rely on each other. This will cause a pressing trace in the surfaces of the said two side walls, which will damage the beauty of the surface of the key cylinder. Furthermore, the key plate 210 will be pressed, bent and deformed if the adjustment of the die set is improper. (3) If the key plate 21 and key cylinder 22 are assembled by means of press work after their electro-plating surface treatments are finished, the electro-plating film on the pressing trace 226 will be broken and removed therefrom. This will damage its beauty and result in corrosion. However, if the key plate 21 and key cylinder 22 are assembled before their electro-plating surface treatments are finished it will be difficult to obtain an even electro-plating surface. (4) When it is in assembly, the key plate and the key cylinder can only be assembled after the protrusion part 212 of the key plate 21 has been slantingly inserted into the rectangular hole 223 of the key cylinder 22 by means of operator's hands, and the inner wall of the small groove 215 between the outward protruding wing 213 and the inward protruding key 214 rests on the end wall of the rectangular hole 223, and the square hole 211 of the plate 210 has been inserted into the cross groove of 224 the solid bar end 221. Hence, an automatic assembly can not be obtained.
The present invention aims at eliminating the above said disadvantages, and provides an improved method of producing a cylindrical key.
The present invention will become fully apparent from the detailed description with reference to the accompanying drawings which are given by way of illustration only, and thus are not limitative of this invention.